What you're suggesting would be a completely pointless, out of the nowhere scene, it would kill off one of the main character for no reason in awkward, badly done manner.

Essentially, we got a Big Lipped Alligator Moment right there.

Even if we ignore the utter lack of worth of this scene, it would defeat the entire purpose of the scene: To make Megatron realize how much he fell of his rank, Megatron doesn't attack Carly exactly because she realizes she has a point [in fact, Megatron growls and raises his fist, but mid-way through he notices she's right and stops to think], that is the entire rhyme and reason of the scene, to have him kill her off means he wasn't listening to what she was saying [specially with that random comeback you suggested], thus his realization makes no sense.

The original scene is "Megatron realizes his decay, and acts accordingly to return to be the big badass", your version is more "Megatron abruptly decides to kill Sentinel because it sounded funny to him".

Personally, I'd have done it so that after Carly says that to Megatron, he then breaks down bawling, sobbing his optics out in guilty admission of what a sham his life's become, until a disgusted Carly yells at him "Oh, suck it up, ya big baby!" Which prompts Megatron to collect himself, taking a deep breath as Carly prompts him on: "This is your chance to take your life back and prove you can make something more of yourself! If you do that, Optimus might actually be willing to accept an offer for a truce!"

He agrees, putting on his best snarly face to confront Sentinel, and stomps off in that direction...as Carly snickers and says under her breath, "Sucker!!! His head'll be off inside five minutes!"